This invention relates generally to hot-fill polyester containers and more particularly to a PET container of this type having hand grip indentations on diametrically opposite sides of the container provided with invertible vacuum collapse surfaces. These surfaces collapse inwardly to accommodate volumetric shrinkage of the container contents following filling with a hot liquid and cool down of the contents.
Thin walled PET containers of bottle shape are becoming increasingly recognized as desirable for containing liquids, such as processed fruit juices and the like, which must be pasteurized, and, as a result, are placed in the container when hot, namely, above about 180.degree. F. Hot fill PET containers are well known. Examples are shown in U.S. Pat. Nos. 4,805,788 and 4,863,046. These containers are characterized by the fact that they are made of a heat set material such as PET with 28-32% crystalinity and they accommodate hot filling and partial evacuation without adverse affects on their appearance. Other hot fill containers are illustrated in earlier filed U.S. patent application Ser. Nos. 211,464; 452,638; and 492,073 owned by the assignee of this application and which have respectively issued as U.S. Pat. Nos. 5,005,716; 4,993,566; and 4,993,567.
These containers are formed by blow molding biaxially orientable polyethylene terephthalate (PET) resin. The result is containers which have a number of advantages such as being lightweight, having excellent mechanical strength, and physical properties, and being inexpensive in cost together with the ability to be produced in large numbers.
Because of the lightweight, thin-walled characteristic of such containers they can be made in large sizes and still be manually handled during storage and dispensing without undue manual effort.
In an earlier filed patent application assigned to the assignee of this application (Ser. No. 663,165, filed Mar. 1, 1991), an improved container of this type is disclosed in which an opposed pair of indentations are formed in the bottle sidewall so as to form hand grip sections. The hand grips enable the container to be grasped between the thumb and fingers of one hand to thereby enable one handed lifting and manipulation of the container. Furthermore, the hand grip indentations in the container are configured and structured so that they will collapse inwardly toward each other to accommodate internal forces tending to collapse the container sidewall inwardly due to filling of the container with liquid at an elevated temperature and subsequent cooling of the liquid. However, the degree of vacuum absorption lost when conventional vacuum absorption panels are replaced by the grip panels may be greater than desired.
The present invention constitutes an improvement on the container shown in the earlier patent application assigned to the assignee of this application in that in the present invention, the hand grip indentations are formed in the blow molded PET container with surface portions that are outwardly bulged in shape. Stated otherwise, the blow molded PET container is initially shaped so that the hand grip indentations are provided with outwardly bulging surfaces which are located outwardly of imaginary vertical planes extending through the container sidewalls.
When the container is filled with hot liquid which is subsequently allowed to cool, the resulting vacuum in the container causes the bulged surfaces to invert and move to positions inwardly of the above described imaginary vertical planes. This results in a reduction in the internal volume of the container which is adequate to compensate for the volumetric shrinkage of the liquid with which the container has been filled. In addition, in the inverted positions of the bulged surfaces, they contribute to the ability of the hand grip indentations to accommodate one-handed gripping and manipulation of the container.
Thus, the present invention utilizes the desirable characteristics of the prior art hot-fill containers and embodies in these containers the pinch grip indentations in a form in which the indentations accommodate the volumetric shrinkage of the container contents. This is accomplished with the initial bulged surfaces in the indentations so that accurate control can be maintained over the extent of volumetric shrinkage that is accommodated. The result is prevention of container sidewall buckling caused by an inability of the container structure to absorb the vacuum induced by volumetric shrinkage.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description, the appended claims and the accompanying drawing.